Issue #13328: Kill mutation for StringLiteralEqualityCheck

Check :-
https://checkstyle.org/config_coding.html#StringLiteralEquality

Mutation :-

Explaination

Reomval of this will not make any issue

the ast

so while entering in the while loop ast is never going to be null so it will alwyas execute.
know lets suppose we have code like

if (s == "a") {}

so the ast look like

    |       |--LITERAL_IF -> if [14:8]
    |       |   |--LPAREN -> ( [14:11]
    |       |   |--EXPR -> EXPR [14:14]
    |       |   |   `--EQUAL -> == [14:14]
    |       |   |       |--IDENT -> s [14:12]
    |       |   |       `--STRING_LITERAL -> "a" [14:17]
    |       |   |--RPAREN -> ) [14:20]
    |       |   `--SLIST -> { [14:22]
    |       |       `--RCURLY -> } [15:8]

our ast would be EQUAL -> == [14:14] and when it enetr the while loop the if will not execute

and result become true which is already set true by

so output will not effect and in the case if

if (s == "a" + "bc") {}
the ast

    |       |   |--EXPR -> EXPR [14:14]
    |       |   |   `--EQUAL -> == [14:14]
    |       |   |       |--IDENT -> s [14:12]
    |       |   |       `--PLUS -> + [14:21]
    |       |   |           |--STRING_LITERAL -> "a" [14:17]
    |       |   |           `--STRING_LITERAL -> "bc" [14:23]
    |       |   |--RPAREN -> ) [14:27]

here plus always become parent if it is used between string literal so if will execute

and it will change ast to TokenTypes.Plus

Know as above explaintaion

if (s == "a") {}

this is also going to be the same as

Regression :-

Report 1 :- https://checkstyle-diff-reports.s3.us-east-2.amazonaws.com/04dd886_2023175346/reports/diff/index.html

Report 2:- https://checkstyle-diff-reports.s3.us-east-2.amazonaws.com/04dd886_2023063730/reports/diff/index.html

Diff Regression config: https://gist.githubusercontent.com/Kevin222004/694cadb00ab976e27fd978d7bc8841a1/raw/8f4e4d48b33f7ccefab4cca495181c0236846380/StringLiteralEquality.xml
Diff Regression projects: https://gist.githubusercontent.com/Kevin222004/9600f179b602d4c971bdb0a050099005/raw/360a95ed7bb60d7a0956e531199d484c4d6f6617/test-projects.properties
Report label: R2